This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-253922, filed Aug. 24, 2000, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a distance measuring apparatus and a distance measuring method, and more specifically, to an improvement of auto-focusing technique for a camera.
2. Description of the Related Art
Broadly speaking, there are two known types of AF (auto-focusing) techniques. One is an active-type such that light from the camera side is projected on subjects to effect distance measuring, while the other is a passive-type that utilizes subject images for distance measuring.
There are commercially available cameras that can carry out distance measuring for subjects in the peripheral portion of the view field, as well as for subjects in the central portion of the view field. However, these cameras have a side effect that miscellaneous subjects, besides a main subject originally targeted by a photographer, can be focused owing to increased distance measuring points.
Described in Jpn. Pat. Appln. KOKAI Publication No. 60-168111 and the like, for example, is a technique that ensures successful photographing by combining the angle of photographic view of the camera and the range of distance measuring.
Despite the increased possible points for distance measuring, however, the information content for focusing is inevitably limited if the distance measuring points are restricted by the angle of photographic view only. If none of the results of distance measuring for selected distance measuring points are reliable, for example, the resulting picture may be entirely defocused in some cases.
Accordingly, an object of the present invention is to provide a distance measuring apparatus and a distance measuring method that can cope with the problem of wrong distance measuring attributable to the presence of miscellaneous subjects and minimize the possibility of defocused photographing.
In order to achieve the above object, according to the present invention, there is provided a distance measuring apparatus comprising: first distance measuring means for effecting distance measuring in accordance with a subject image signal for the central portion of a view field; second distance measuring means for projecting distance measuring signal light on a subject in the central portion of the view field and effecting distance measuring in accordance with a reflection of the distance measuring signal light from the subject; third distance measuring means for effecting distance measuring in accordance with image signals for the peripheral portion of the view field; and decision means for determining whether or not to use the result of distance measuring obtained by means of the third distance measuring means, in accordance with the output results of the first and second distance measuring means.
According to the invention, moreover, there is provided a distance measuring apparatus comprising: a first sensor array located for distance measuring for the central portion of a view field and including a fixed-light eliminator; and a second sensor array located around the first sensor array and including no fixed-light eliminator.
According to the invention, furthermore, there is provided a distance measuring method comprising: a first step of executing active-type distance measuring operation and passive-type distance measuring operation for the central portion of a view filed; a second step of determining whether or not neither of the active- and passive-type distance measuring operations is executable for the central portion of the view filed; and a third step of executing the passive-type distance measuring operation for the peripheral portion of the view filed only if it is concluded in the second step that neither of the distance measuring operations is executable.
According to the invention, moreover, there is provided a distance measuring apparatus comprising: a first sensor array for detecting a subject image signal for the central portion of a view field; a projecting element for projecting light on a subject in the central portion of the view field through a projection optical system; a second sensor array for detecting subject images in the peripheral portion of the view field; an A/D converter for converting output signals from the first and second sensor arrays into digital values; and a CPU for settling the focus position of a photographic lens in accordance with the digital data converted by means of the A/D converter, the CPU being adapted to use the output of the second sensor array only if distance measuring cannot be effected with use of the output of the first sensor array, without regard to the execution of the projection by means of the projecting element.
According to the invention, furthermore, there is provided a distance measuring method comprising: a first step of executing photographing distance measuring for the central portion of a view filed; a second step of determining whether or not the reliability of the result of distance measuring obtained in the first step is low; a third step of using the result of distance measuring obtained in the first step if it is concluded in the second step that the reliability is high; a fourth step of executing active-type distance measuring for the central portion of the view field and passive-type distance measuring for the peripheral portion of the view filed if it is concluded in the second step that the reliability is low; and a fifth step of comparing two results of distance measuring obtained in the fourth step and using the result of distance measuring for the far side.
Since active-type AF utilizes a reflection of projected light, accurate distance measuring cannot be effected for subjects in the distance from which the projected light cannot return or low-reflectance subjects. However, it is an effective distance measuring system for noncontrastive subjects or dark scenes that cannot be favorably coped with by passive-type AF.
On the other hand, the passive-type AF is a distance measuring system that utilizes image signals of subjects. In this case, therefore, there is no possibility of lowering of accuracy attributable to the subject distance, which is involved in the active-type AF, although the accuracy can be changed by the contrast or brightness of subjects.
Accordingly, it has been attempted to develop cameras or other focusing apparatuses that can focus subjects without preference by combining the two distance measuring systems. However, no effective countermeasures are taken against awkward scenes for either of the two systems to deal with.
According to the present invention, distance measuring can be securely effected by combining the two systems for the main subject in the central portion that hardly allows the presence of miscellaneous subjects. For those scenes with which neither of the two distance measuring systems can deal well, on the other hand, photographing with less defocusing can be enjoyed also with reference to the other results of distance measuring than those of distance measuring for the central portion of the view field.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.